The present invention concerns a clamping roller switch gear which is classed as an infinitely variable step-by-step switch gear. A drive element and a driven element define, together with opposing clamping surfaces, wedge-shaped clamping gaps which taper in opposite directions and in which clamping rollers are arranged. Housing-fixed stops are provided which keep the clamping rollers disengaged from the clamping surfaces when the drive element of the clamping roller switch gear is not activated. In this way, it is assured that the driven element is rotatable in an idling or in an initial position of the drive element. If the drive element is moved out of its initial or idling position, the drive element effects a work stroke. The return movement of the drive element into the initial position is an idling stroke during which the driven element is not activated. During the work stroke of the drive element in the one direction, the one damping rollers are brought into clamping engagement with the clamping surfaces, while the respective other clamping rollers are fixedly supported on the housing and remain disengaged from the clamping surfaces. During the idling stroke, those clamping rollers that were previously clamped are disengaged from the clamping surfaces due to the reversal of movement, while the other clamping rollers remain supported on the housing-fixed stops and disengaged from the clamping surfaces even during the idling stroke. Therefore, no entrainment of the driven element takes place during the idling stroke.
A clamping roller switch gear is known, for example, from EP 0 631 901 B1. This document discloses an adjusting device, particularly for adjusting a seat of a motor vehicle. In this device, a clamping roller switch gear (FIGS. 2 and 3 of EP 0 631 901 B1) and a clamping roller locking gear (FIG. 13 of EP 0 631 901 B1) are coupled to each other. FIG. 2 of EP 0 631 901 B1 shows the clamping roller locking gear in an initial position in which the pivoting lever is not actuated, and FIG. 3 of EP 0 631 901 B1 shows the pivoting lever displaced in one direction up to the end of its work stroke. The clamping roller switch gear comprises an inner element that engages into an opening of the pivoting lever. The clamping rollers are arranged in an annular space defined by the pivoting lever and the inner element. By an appropriate configuration of the recess, the annular space is radially constricted at a plurality of circumferentially spaced sections. The clear distance between the cylindrical peripheral surface of the inner element and the wall of the recess in these sections is smaller than the diameter of the clamping rollers. In this way, wedge-shaped clamping gaps are formed into which the clamping rollers are biased by compression springs. The clamping rollers are pressed against housing-fixed stops that are provided between every two adjacent clamping rollers. The tapered ends of the wedge-shaped clamping gaps. of the two clamping rollers face each other. The housing-fixed stops are dimensioned so that the clamping rollers are not in clamping engagement with their clamping surfaces. If, as shown in FIG. 3 of EP 0 631 901 B1, the pivoting lever is displaced in clockwise direction out of its initial position, those clamping rollers are drawn into their clamping gaps whose tapered ends are oriented in anti-clockwise direction. Now, an entrainment of the inner element takes place. During this entrainment, the compression springs arranged between every two clamping rollers are compressed till the spring coils come to bear against each other as a block. In the block state of the compression springs, the work stroke of the pivoting lever is terminated. During the work stroke, the respective other clamping rollers remain supported on the housing-fixed stops, and both the inner element and the pivoting lever are displaced past these clamping rollers that are supported on the housing-fixed stops. A possible drawback of this arrangement is that the clamping rollers supported on the housing-fixed stops during the work stroke get pressed against the wall of the recess or against the peripheral surface of the inner element, for example, due to the spring force. This friction contact is a drawback because, among other things, it considerably increases the force required for carrying out a work stroke. If such a clamping roller switch gear is used in a height adjusting device of a motor vehicle seat, for example, it is desirable that the seat height adjusting operation runs smoothly and with ease. A further possible drawback of this prior art is that clamping rollers that are supported on the housing-fixed stops during the work stroke may be forced out of their clamping gaps. This means that guides for the clamping rollers would have to be provided adjacent the clamping gaps.
The object of the present invention is therefore to provide a clamping roller switch gear according to the preamble of claim 1 wherein the clamping rollers that are supported on housing-fixed stops during the work stroke remain in their clamping gaps. The invention achieves this object by the fact that the drive element comprises two drive members that are rotatable in opposite directions, in the initial position of the drive element, both these drive members are supported on housing-fixed stops, and when the pivoting lever is pivoted out of its initial position in one direction of pivot it positively entrains one of the two drive members and when pivoted out of its initial position in the opposite direction of pivot, the pivoting lever positively entrains the other of the two drive members. The invention therefore achieves that the clamping rollers supported on housing-fixed stops during the work stroke remain fixedly supported on the housing together with their drive member. This means that the released clamping rollers do not leave their clamping gap. The clamping gap can be dimensioned so that the clamping rollers that are fixedly supported on the housing remain out of contact with the driven element that is rotated during the work stroke. Advantageously, compression springs may be arranged in the clamping gaps and be supported at one end on the drive member and at the other end on the clamping roller, and the spring force of these springs presses the clamping rollers against the first housing-fixed stop. According to a further advantageous feature of the invention, the first housing-fixed stop has a concave contour matched to the peripheral surface of the clamping rollers so that the clamping rollers are perfectly retained on this concave contour. Thus, in the initial position of the clamping roller switch gear, the clamping rollers are gripped between these springs and the first housing-fixed stops. Undesired chattering noises are thus totally excluded.
Each of the drive members comprises at least one clamping ramp forming one of the clamping surfaces, and the wedge-shaped clamping gaps defined by the clamping ramps of one of the drive members taper in the one direction, while the clamping gaps defined by the clamping ramps of the other drive member taper in the opposite direction. This assures that an entrainment of the driven element is possible in both directions of rotation. Preferably, the tapered ends of two adjacent wedge-shaped clamping gaps, each of which is defined by one of the two drive members, are oriented towards each other, and the first housing-fixed stop engages between the two wedge-shaped clamping gaps thus keeping the clamping rollers that are arranged in these clamping gaps out of clamping engagement in the idling initial position of the drive element. The first housing-fixed stops can be formed, for example, by tongues fixed on a housing.
Preferably, the drive element comprises a switch disk that is connected rotationally fast to the pivoting lever and that entrains one of the drive members in the one direction, and the other drive member in the other direction. The switch disk can comprise slots, for example, into which pins fixed on the drive members engage. In the initial position of the pivoting lever, the pins of the one drive member bear against one end of the slots and the pins of the other drive member bear against an opposite end of the slots. Only one pin engages into each slot. When the pivoting lever is displaced, one of the two drive members, depending on the direction of pivot, is positively entrained.
According to a further particularly advantageous feature of the invention, in the idling initial position of the drive element, one drive member is pressed by spring force against a second housing-fixed stop and the other drive member is pressed by spring force against a third housing-fixed stop. In this way, for example, undesired chattering noises of the drive members are excluded. These additional housing-fixed stops can be formed, for example, in that the mentioned pins of the drive members engage into slots of the housing. In the initial position of the pivoting lever, the pins of one of the drive members bear against one end of the slots and the pins of the other drive member bear against an opposite end of the slots. Only one pin engages into each slot. The spring force can be further used for biasing the drive members out of their displaced positions into their initial positions under the action of the spring force. This means that a pivoting of the pivoting lever is effected in opposition to this spring force, and releasing the pivoting lever has the consequence that the pivoting lever is biased into its initial position by this spring force.
The two drive members can be mounted axially behind each other for pivoting about a common axis of pivot. This arrangement makes it possible to arrange a plurality of circumferentially spaced, radially projecting fingers on each of the drive members with at least one finger of the one drive member and at least one finger of the other drive member engaging with switching clearance in peripheral direction between two circumferentially adjacent fingers of the respective other drive member. The switching clearance is dimensioned so that the angle of pivot between these inter-engaging fingers just about corresponds to the maximum work stroke of the pivoting lever. In this arrangement, it is possible without any problem to configure the inter-engaging fingers so that the finger of the drive member that is displaced through a switching stroke comes to abut against an adjacent finger of the other drive member that is supported on its housing-fixed stop. In contrast to the prior art discussed above, the end of the work stroke is not determined by a block state of springs but by positive stops without the danger of damage to a spring.
According to another advantageous feature of the invention, a compression spring is arranged between every two adjacent inter-engaging fingers, with one end of the springs being supported on one of the fingers, and the other end of the springs being supported on the other finger. These compression springs bias the two drive members against their associated second and third housing-fixed stops. Although the spring force of only one compression spring can already be sufficient, it can be appropriate in some cases to arrange a plurality of springs between every two inter-engaging claws. In this way, the total spring force is increased by the spring force of each additionally provided spring.
According to a further proposition of the invention, the driven element comprises an annular driven member having a cylindrical clamping track defined on its inner peripheral surface. In this arrangement, the aforesaid fingers of the two drive members can comprise the clamping ramps which together with the cylindrical clamping track of the annular driven member define the wedge-shaped clamping gaps.
According to still another proposition of the invention, the clamping roller switch gear is arranged in a housing fixed to a frame, the driven member being mounted in the housing through a radial bearing. For one thing, the housing therefore assumes the function of protecting the clamping roller switch gear from the ingress of undesired foreign matter and for another, it serves for the described radial mounting. A particularly simple radial bearing can be formed in that the driven member comprises a circumferentially extending sliding bearing surface that is radially mounted on the inner wall of the housing which is likewise configured as a sliding bearing surface.
Sliding bearing surfaces can be configured on the fingers of the drive members and be in sliding contact with a sliding bearing surface configured on the inner peripheral surface of the driven member. In this simple manner, the drive member can be radially mounted and centered relative to the driven member.
The sliding bearings primarily serve the purpose of centering. The sliding bearing surfaces can therefore also be designated as centering surfaces that are suitable for sliding contact. The outer peripheral surface of a cylinder, for example, that is in line contact with another outer peripheral surface can also be considered as a centering surface in the present context.